It may have been a few centuries since Switzerland fought a war, but it still enjoys a reputation as a place that would be pretty difficult to invade.

Its "mountain redoubt" isn't quite what it was in Cold War days, but the country still "maintains a system of about 26,000 bunkers and fortifications throughout the Swiss Alps meant to deter attacking armies."

Get past the Alps, and you have to deal with a population where all men - and many women - have military training, and quite a few have held on to their assault rifles just in case.

But fortress Switzerland's reputation for impregnability took a blow this week, when an Ethiopian Airlines flight was hijacked by its asylum-seeking co-pilot and landed in Geneva. While Italian and French fighter planes were scrambled to escort the hijacked airliner through their airspaces, Switzerland's own F-18s remained on the ground throughout the incident.

Why? According to Swiss Air Force spokesman Laurent Savary, as reported by Agence France-Presse, it was after business hours:

The Swiss airforce is only available during office hours. These are reported to be from 8am until noon, then 1:30 to 5pm. "Switzerland cannot intervene because its airbases are closed at night and on the weekend," he said, adding: "It's a question of budget and staffing."

So, if planning an aerial invasion of Switzerland, nights, weekends and lunchtimes are probably your best bet.

Take note, Liechtenstein.

Joshua Keating is a staff writer at Slate focusing on international news, social science and related topics.